This application makes reference to, incorporates the same herein, and claims all benefits accruing under 35 U.S.C. xc2xa7119 from an application for HEATING ROLLER ASSEMBLY FOR ELECTROPHOTOGRAPHIC PRINTER earlier filed in the Korean Industrial Property Office on Feb. 22, 2001 and there duly assigned Ser. No. 9038/2001 by that Office.
1. Field of the Invention
The present invention relates to a heating roller assembly in an electrophotographic printer for fixing a toner or developed image on a printing medium, and more particularly, to a direct-heating type heating roller assembly including a power connecting member mounted on both a heating layer and a protective layer.
2. Description of the Related Art
Printers have been provided with a direct-heating type fixing roller assembly for fixing a toner image or a developed image on a printing medium. The direct heating type fixing roller assembly defines a roller body and a current resistance heating layer formed around a cylindrical circumferential outer surface of the roller body. Typically, a pair of electrically conductive power connecting members having a hollow ring shape and coupled to a terminal of an external power source are inserted around the roller body and connected to the current resistance heating layer to supply power to the heating layer and to heat the heating roller assembly to a predetermined high temperature for fixing the image on the printing medium.
The power connecting member, however, becomes damaged due to the mechanical pressure applied to the fixing roller when the power connecting member is heated to the high temperature from a room temperature in a very short period of time for quick-heating and fixing the printing image on the printing medium during the operation of the printer. The damaged power connecting member causes an electrical disconnection between the heating layer and the power connecting member.
Moreover, due to the repeatedly exerted thermal shock and electrical shock, a great extent of stress is exerted on the power connecting member. Thus, durability of the power connecting member becomes deteriorated as cracks are developed in the power connecting member and the heating layer. Furthermore, it is not safe but dangerous when sparks are generated in the cracks of the damaged power connecting members and the heating layer.
To solve these and other problems in the art, it is an object of the present invention to provide an improved heating roller assembly.
It is another object to provide an improved power connecting member mounted on a roller body of a heating roller assembly.
It is still another object to provide a heating roller assembly able to prevent a power connecting member from being damaged due to mechanical shock exerted on the power connecting member.
It is yet another object to provide a heating roller assembly able to reduce thermal shock applied to a power connecting member mounted on the heating roller assembly.
It is still yet another object to provide a heating roller assembly able to prevent a electrical disconnection between a heating roller and a power connecting member.
It is also an object to provide a heating roller assembly able to improve durability and stability of the electric contact between a power connecting member and a heating layer generating heat for fusing and fixing a toner image on a printing medium.
To achieve these and other objects of the present invention, there is provided a heating roller assembly including a roller body and at least one power connecting member mounted around the roller body. The roller body includes a cylindrical body having an axial axis, a protective layer deposited on a circumferential outer surface of the cylindrical body, and a heating layer disposed between the cylindrical body and the protective layer and having terminal portions formed on each end of the heating layer. An inner protective layer is disposed between the heating layer and the cylindrical body.
The power connecting member is disposed around the terminal portion of the heating layer to be put in contact with the terminal portion of the heating layer, thereby supplying power to the heating layer. The heating roller assembly includes a stress distribution means formed on a circumferential inner surface of the power connecting member for dispersing thermal or mechanical stress exerted on the power connecting member during rotation of the heating roller assembly or during heating the heating layer.
The stress distribution means includes a plurality of elevated surfaces formed on a cylindrical circumferential inner surface of the power connecting member facing the roller body. Each elevated surface of the stress distribution means has a radial distance from the axial axis of the cylindrical body and is formed along the cylindrical circumferential inner surface in a circular direction. The radial distances of the elevated surfaces are different from each other. The elevated structure of the stress distribution means corresponds to an elevated structure of the heating layer and the protective layer.
The outer protective layer has a length in the axial direction less than the heating layer so that an end portion of the outer protective layer does not cover the terminal portion of the heating layer. The end portion of the protective layer and the terminal portion of the heating layer are surrounded by respective elevated surfaces of the stress distribution means of the power connecting member. A first elevated surface of the stress distribution means surrounds the cylindrical outer surface of the terminal portion of the heating layer while a second elevated surface of the stress distribution means surrounds a cylindrical outer surface of the end portion of the protective layer. Since a thickness of the power connecting member in the axial direction of the cylindrical body is greater than the terminal portion of the heating layer, the power connecting member surrounds the end portion of the protective layer. A vertical side formed between the first and second elevated surfaces of the stress distribution means is disposed to face a distal end surface of the protective layer. A bonding layer made of a conductive material is disposed between the elevated surfaces of the power connecting member and the terminal portion of the heating layer or the end portion of the protective layer.
In a second embodiment, it is preferred that the protective layer includes an outer insulating layer disposed on the heating layer, an adhesive layer disposed on the outer insulating layer, and a coating layer disposed on the adhesive layer. An end portion of the outer insulating layer is covered by the second elevated surface of the stress distribution means. The bonding layer made of the conductive material is disposed between the first elevated surfaces of the stress distribution means and the terminal portion of the heating layer and between the second elevated surface and the end portion of the outer insulating layer of the protective layer.
In a third embodiment, it is preferred that the outer insulating layer, the adhesive layer, and the coating layer of the protective layer have the same length in the axial direction. The length of the protective layer is less than the heating layer. While the first elevated surface of the stress distribution means covers the terminal portion of the heating layer, the second elevated surface of the stress distribution means of the power connecting member surrounds the end portion of the coating layer which forms an outer circumferential surface of the roller body. The distal end surfaces of the outer insulating layer, the adhesive layer, and the coating layer of the protective layer are surrounded by the vertical side of the stress distribution means of the power connecting member. The bonding layer made of the conductive material is disposed between the elevated surfaces of the stress distribution means and each one of the terminal portion of the heating layer, the end portions of the coating layer, the outer insulating layer, the distal ends surfaces of the protective layer. Furthermore, it is preferred that the heating layer includes a plurality of heating layers which are sequentially disposed around the cylindrical body, and that terminal portions of the heating layers are surrounded by each one of a pair of the first elevated surfaces of the stress distribution means.
In a fourth embodiment, it is preferred that the stress distribution means has an inclined inner surface having an angle with respect to the cylindrical circumferential outer surface of the cylindrical body. The stress distribution means is line-contact with an edge portion of the heating layer while a conductive bonding material is filled between the inclined inner surface of the power connecting member and the terminal portion of the heating layer and the end portion of the protective layer except the portion of the line contact formed between the slant inner surface of the power connecting member and the edge portion of the heating layer.